Valuables such as jewelry, stocks and bonds, and classified material, are typically stored in safes., Such safes usually have a mechanism that may be actuated by providing a preselected combination to open a combination lock mounted to the door of the safe. Some safes require the use of a key in lieu of or addition to a combination. Unfortunately, sometimes the required combination is forgotten, written and then lost or otherwise unavailable due to the absence of the individual possessing it. Where a key is required to open the safe door, the key itself may sometimes be lost or otherwise unavailable. In such circumstances, an irregular entry, i.e., other than by normal unlocking of the lock mechanism in the door, is usually made by a technician who drills a small hole through the door near the lock and utilizes special tools inserted through the hole to facilitate actuation of the locking mechanism to its open position. Burglars, too, may use such a technique. In either case, typically, a hole approximately 1/4" in diameter is drilled through one or more layers forming the thickness of the safe door. A tool is then inserted through the hole to enable visual observation of a tumbler mechanism of the lock or a lock picking tool may be inserted to manipulate the tumblers. Whether the irregular entry into the safe in this manner was effected for justifiable reasons or in the course of a burglary, the physical integrity of the safe must be restored for its future use.
One known technique for restoring safe integrity, when such a hole or access-aperture has been formed therein, is to insert a plug made of a tough weldable material into the hole and to then weld around an outside end of the plug to the outermost wall through which the hole was drilled. A known plug of this type has a slight uniform taper along its entire length, with an insertable end diameter smaller than the original hole diameter in the outer wall, and an outside end having a diameter larger than the hole diameter. This uniformly tapered elongate plug is typically hammered into place, so that it is lodged into the outermost layer of the safe door, and is then welded to the outside of the outermost layer. Unfortunately, entry through the same hole can be made readily by a person applying a drill equal to at least the diameter of the original hole into which the plug is lodged. Once such drilling passes the outside welded portion of the plug, because of the lengthwise taper of the plug, the plug can simply be tapped into the safe and the hole becomes available for reuse enabling access to the safe contents.
Safes for storing particularly valuable materials routinely have multi-layer walls in which the different layers have different properties. For example, the outermost layer of such a safe may be formed of a 1/2" thick sheet of a tough alloy steel that is not readily cracked even under repeated heavy blows. Such materials, however, can be drilled through with an appropriately selected drill bit. One or more layers of a fire-retardant material may also be provided inside of the outermost tough alloy layer. Further inside the safe, there may be provided a layer of a particularly hard material selected for its inherent tendency to slow down any drilling therethrough. However, to form substantially sized plates of such hard material, some sacrifice in the total hardness of the material becomes necessary. Accordingly, such hard materials do not present an insuperable problem, and can be drilled through by the use of a succession of drill bits selected for drilling through hard materials.
To prevent irregular access by the easy drilling out of the elongate uniformly tapered plug, an improvement consists in forming an axially oriented through-hole in the plug and filling the through-hole with a mixture of a powdered carbide material and powdered brass or the like. The plug is then heated to a point where the powdered brass melts and bonds around the carbide materials and the wall of the through-hole to, hopefully, fill the entire through hole. In principle, such a device should tend to readily blunt most drill bits because the carbide material is extremely hard and difficult-to-machine. A major problem with this approach is that it is very difficult to ensure that the through-hole formed through the plug is uniformly and totally filled with the mixture of carbide material and brass. In practice, voids may be formed within the through-hole of the plug, and it is not possible to readily determine which plugs have such voids and are, therefore, not as effective as desirable.
Reference at this stage may be had to FIGS. 1-3 which illustrate, respectively, an outside elevation, an end elevation, and a longitudinal cross-sectional view of such a known carbide-filled tapered elongate element 20 in place inside a hole drilled through two layers 30, 40 in a wall of a safe. It will be understood that for such an element 20, its overall length a.sub.1 and its maximum diameter d.sub.1 must be selected such that when a length a.sub.2 thereof is inserted as far as possible from the outside of outer layer 30 into a hole of diameter d.sub.5, a portion of length (a.sub.1 -a.sub.2) remains outside and allows weld material 22 to be deposited therearound. Under ideal circumstances, the through-hole of diameter d.sub.3 in element 20 should be completely filled. Unfortunately, the carbide/brass material 24, as best seen in FIG. 3, is not uniformly distributed but has voids 26 formed therein. Voids 26 are exaggerated in size to illustrate them clearly in FIG. 3. The presence of such voids is highly undesirable. As is readily understood from FIG. 3, if a person drills away only to a short distance into thickness d.sub.0 of outer layer 30, most of the inserted length of element 20 will simply fall or be readily pushed through access-aperture of diameter d.sub.5 through both of layers 30 and 40.